The 13C spin-lattice relaxation times (T1's) of polyisobutylenes (PIBs) bearing tert-Bu, tert-chloride, exo-olefin, alc., aldehyde, and acetal end groups have been detd., and all the signals in their 13C-NMR spectra were assigned according to the gradient of T1 along the polymer chain with the min. in the middle. 13C T1 anal. has also been used to obtain assignments for internal polyisobutylene segments adjacent to arom. initiator residues. The method provides insight into the interaction of hydroxyl end groups of alc.-capped PIBs, and allows identification of the low mol. wt. impurities in the polymers. Assignments of all the 1H NMR signals of the above polyisobutylenes were obtained by 2D 1H-13C HETCOR spectroscopy. For some polymers, 1H-NMR signals were also assigned based on their 1H T1 values and the assignments agree with those generated by HETCOR spectroscopy.